1. Field of the Invention
This invention relates to nozzles for controlling the directional flow and fine atomization of liquids expelled therethrough, and more particularly to nozzles used for atomizing fuel before injection into an internal combustion engine.
2. Prior Art
Stringent emission standards for internal combustion engines suggest the use of advanced fuel metering techniques that provide precise delivery of atomized fuel into a localized volume or area of the manifold or engine. Such precise delivery of the fuel not only improves the emission quality of the exhaust, but also improves the cold start capabilities, fuel consumption and performance. The quality of atomization of the fuel, which includes both cone angle and fuel droplet size, is a significant factor in overall engine performance.
Meaningful improvements in performance and emissions levels can be achieved by controlling the cone angle of the atomized fuel injected into the manifold. As used herein, the term cone angle is defined as the angle of the atomized spray with respect to the central axis of the injector or one of the major orifices defining the injector.
In most engine designs it is desirable to focus the atomized fuel throughout the central portion of the intake manifold so that it will not wet the cylinder walls. In other cases, a more diffused cone angle can allow improved performance in engines requiring specific combustion chamber configurations.
Smaller fuel droplets generally have greater volumes of surrounding air as required to complete the combustion process. Smaller fuel droplets also promote a more homogeneous mixture of fuel and air, which in turn provides a faster, more complete combustion process. This improved combustion process reduces hydrocarbon (HC) and carbon monoxide (CO) emissions which are generally caused by localized high fuel to air ratios produced from heterogeneous injector sprays.
Micromachined fuel injectors have the potential for realizing significant improvements in the quality of the atomized fuel utilized by the internal combustion engine. As an example of silicon micromachined (SMM) devices that are used for atomizing liquids, U.S. Pat. No. 4,828,184 discloses the use of silicon plates having openings for metering the fuel flow. A first opening in a first silicon plate is offset from a second opening in a second silicon plate juxtaposed with the first silicon plate. The area between the first and second openings has a reduced thickness so as to form a shear gap for accelerating the flow of the fuel through opposing shear gaps in a direction substantially parallel to plane of the first and second plates. Such shear flow causes turbulence and liquid dispersion advantages for atomizing the fuel before it is propelled into the combustion chamber of an internal combustion engine.